CHARLESTON, W.Va. -- Democratic candidates hoping to fill Jay Rockefeller's U.S. Senate seat must be tenacious campaigners, secure support from state and national party leaders and raise massive amounts of money, political observers said Friday.

The winner in the Democratic primary likely would face U.S. Rep. Shelley Moore Capito, the only Republican yet to announce plans to run for the Senate seat in 2014.

"This is going to be an aggressive and high-finance campaign," said Kanawha County Commission President Kent Carper. "They better have it all. Getting through the primary is going to be a battle royal."

The names of numerous potential Democratic candidates were tossed around after Rockefeller announced Friday that he would not seek re-election.

At the top of the list: former West Virginia Gov. Gaston Caperton.

Caperton, who lives in Charleston, served 13 years as president of the College Board, which administers SAT and AP exams. He was in New York on Friday and declined comment.

Caperton said he plans to attend Gov. Earl Ray Tomblin's inaugural on Monday and might discuss his plans next week. "If he's interested," Carper said of Caperton, "he would be formidable."

Other possible candidates mentioned include:

• Carte Goodwin, who was appointed U.S. senator after Sen. Robert C. Byrd, D-W.Va., died in 2010. Goodwin now works as a lawyer in Charleston. His wife, Rocky, is a senior aide to Rockefeller.

Goodwin, who declined to run for the Senate seat now held by Sen. Joe Manchin, D-W.Va., would not say if he would seek Rockefeller's seat.

"Today is Senator Rockefeller's day," said Goodwin, who attended Rockefeller's news conference Friday. "While serving in the Senate, I learned firsthand about Senator Rockefeller's passion and dedication. Today, we're celebrating his 50 years of public service."

• Retired Adjutant General Allen E. Tackett, who headed the West Virginia National Guard. Tackett was a close friend of Byrd.

• West Virginia Secretary of State Natalie Tennant, who said Friday she would give the U.S. Senate run "strong consideration."

"I haven't ruled anything in or anything out," Tennant said. "I'm honored to be considered as a person who would follow in [Rockefeller's] footsteps."

• Ralph Baxter, CEO of Orrick, Herrington & Sutcliffe, one of the world's largest law firms, with more than 1,100 attorneys. San Francisco-based Orrick has a Global Operations Center in Wheeling. Baxter, who lived in West Virginia as a boy, serves on the West Virginia Workforce Investment Council and as a board member of the West Virginia Education Alliance.

Other potential candidates are state Sen. Corey Palumbo, Senate President Jeff Kessler, former Democratic Party chairmen Nick Casey and Mike Callaghan, U.S. Rep. Nick Rahall, state Sen. Erik Wells, D-Kanawha, and former state Sen. Jim Humphreys.

"The list of people who will talk about running will be large," Carper said.

Several political observers suggested that Supreme Court Justice Robin Davis might consider a run, but the court's rules would require her to step down as a justice if she entered the race -- something that's unlikely to happen.

Political consultants predicted a small field of Democratic candidates if Caperton decides to run, and a larger group if he does not.

Mike Plante, who has run numerous campaigns for Democrats, said a conservative Democrat who supports the coal industry would have the best chance of winning the primary and beating Capito.

"They would have to carve out an identity that they're an independent-minded, West Virginia Democrat, not a Washington Democrat," said Plante. "They need to be pro-coal and conservative on social issues."

Democratic Party Chairman Larry Puccio said people "extremely interested" in running contacted him Friday. He declined to name them.

Puccio predicted that the U.S. Senate Democratic primary would be competitive, and unsuccessful candidates likely would support the winner.

"We showed that when the candidates supported Governor [Earl Ray] Tomblin last time," Puccio said Friday. "The winning candidate will be someone who people believe in. I think we'll be very successful in that election."

Carper said whoever runs must secure support from national as well as state Democratic Party leaders.

Candidates also must have tremendous personal wealth or be able to raise millions of dollars, political observers said.

"This will be the most expensive Senate race in the history of West Virginia," Carper said. "The race has national implications. At the end of the day, this is going to be about money."

The 2016 West Virginia gubernatorial race also could factor into the 2014 U.S. Senate race. Democratic candidates might run for Rockefeller's seat to make their names more recognizable with voters, then start a run for governor soon after.

"It certainly would be an opportunity to build some name recognition," said Chris Stadelman, vice president of The Manahan Group, a political consulting firm in West Virginia. "There's going to be a wide field -- not only for the Senate race in 2014 but for others, looking ahead to 2016.

Stadelman expects Democratic candidates to start announcing plans to run for the Senate in the coming weeks.

So far, Capito has no opposition in the GOP primary, but U.S. Rep. David McKinley has said he has not ruled out running against Capito. McKinley issued a statement praising Rockefeller Friday, but he did not say if he would run for the senator's open seat.

"There's going to be so much money involved in this race on both sides," Stadelman said, "so you have to announce fairly quickly so you can start raising money."

Carper said the winner of the Democratic primary would be someone who can raise money from national groups while also waging an aggressive grassroots campaign across West Virginia.

"They better have a fire in the belly," he said. "It has to be a tenacious campaigner."

And if there's consensus among Democrats it's this: Capito will be tough to beat. She's never lost an election.

"We were hoping that Senator Rockefeller would run again," said Bob Brown, executive director of the West Virginia School Service Personnel Association. "It's going to take a lot of money to beat Shelley."